Field of the Invention
The present invention relates to a nozzle for an injection molding machine.
Description of the Related Art
An injection molding machine generally comprises a mold clamping mechanism section and an injection mechanism section that are disposed on a machine base. The injection mechanism section serves to heat and melt a resin material (pellets) and inject the resulting molten resin into a cavity of a mold. The mold clamping mechanism section mainly serves to open and close the mold.
In the mold clamping mechanism section, a fixed platen, a movable platen, and a rear platen disposed behind the movable platen are connected by a plurality of tie rods. The movable platen and the rear platen move along the tie rods. A mold is attached to each of opposite working surfaces of the fixed and movable platens and mold clamping and opening operations are performed.
In the injection mechanism section, an injection unit is advanced and retracted relative to the fixed platen, a nozzle on the distal end of an injection cylinder of the injection unit is brought into close contact with a resin injection port of the fixed platen, and the resin is supplied through the injection cylinder. The injection mechanism section is provided with a nozzle touch mechanism for bringing the nozzle on the cylinder end into close contact with or separating it from the resin injection port of the fixed platen. The nozzle on the distal end of the injection cylinder is configured to be pressed against the resin injection port of the fixed platen by the nozzle touch mechanism during continuous molding operation.
FIG. 6 is a view showing a part configuration around the nozzle of the injection mechanism section. A nozzle 2 is disposed in front of a cylinder 1, and the cylinder 1 and the nozzle 2 are secured to each other by bolts 3. The cylinder 1 and the nozzle 2 are located face to face with each other. Numeral 7 denotes mating surfaces of these two members. A molten resin supplied from a hopper (not shown) is fed to the resin injection port of the fixed platen through a molten resin passage 6. Heaters 4 and 5 are wound on the outer-diameter portions of the cylinder 1 and the nozzle 2, respectively. The temperatures of the cylinder 1 and the nozzle 2 are controlled by energizing the heaters 4 and 5.
Gas may be generated from the molten resin in the molten resin passage 6 in some cases. If the generated gas gets into a mold, it may affect a molded article and possibly cause poor appearance or reduced strength of the molded article. Preferably, therefore, the gas should be prevented from getting into the mold. To attain this, the cylinder 1 or the nozzle 2 is provided with an exhaust port through which the gas can be removed. As shown in FIG. 6, a small gap or exhaust groove 8 is formed between mating surfaces of the cylinder 1 and the nozzle 2.
A CD-ROM of Japanese Utility Model Application No. 3-53856 (Japanese Utility Model Application Laid-Open No. 5-7423) discloses a technique in which a nozzle for an injection molding machine is divided into a proximal portion and a distal end portion, and a resin passage in a nozzle body is formed with a gas vent passage that prevents leakage of resin but allows passage of gas.
Japanese Registered Utility Model Publication No. 3014793 discloses a technique in which a nozzle of an injection molding machine is provided with radial degassing grooves on contact surfaces of the nozzle and a heating cylinder. The degassing grooves communicate with an annular vacant space defined by an annular step portion on the outer periphery of the nozzle. Further, the heating cylinder is provided with a communication hole through which the annular vacant space opens to the atmosphere such that gas can be discharged in the radial direction of the cylinder.
Japanese Patent Application Laid-Open No. 11-170320 discloses a technique in which an injection unit of an injection molding machine is provided with a ring-shaped, porous gas discharge member through which gas generated in the injection unit can be discharged to the outside.
In the technique shown in FIG. 6, the heater 4 is located on the outer-diameter portion of the cylinder 1 so as to cover the greater part of it. Therefore, the location of the exhaust groove 8 is inevitably limited to an area where the heater 4 is not located, possibly affecting the cylinder temperature control by the heater 4. If the heater 4 is located so as to cover the exhaust groove 8, in contrast, gas cannot be discharged smoothly through the exhaust groove 8 and may stagnate in the cylinder 1, thereby corroding the heater 4 and its surrounding members in some cases.
In the technique disclosed in the CD-ROM of Japanese Utility Model Application No. 3-53856 (Japanese Utility Model Application Laid-Open No. 5-7423), the gas vent passage is formed in the nozzle that is divided into the proximal portion and the distal end portion. Thus, the nozzle must be divided into the proximal portion and the distal end portion in order to form the gas vent passage, so that it may be more complicated in structure and higher in cost than a one-piece nozzle.
In the technique disclosed in Japanese Registered Utility Model Publication No. 3014793, as in the technique shown in FIG. 6, the gas is discharged in the radial direction of the cylinder. Possibly, therefore, the location of the gas vent passage is limited to an area where no heater is wound on the cylinder, or the gas may stagnate in a gas vent passage, if the gas vent passage is closed by a heater.
In the technique disclosed in Japanese Patent Application Laid-Open No. 11-170320, a nozzle must be formed using a porous component, which is a dedicated member for gas venting.